This invention relates to brush seals for sealing between adjacent components and, more particularly, relates to brush seals for use in high temperature environments, such as between shrouds and bucket tips or covers in gas or steam turbines, and requiring cooling by a cooling medium.
Brush seals are increasingly being used in gas and steam turbine applications. In many instances, brush seals are being installed in lieu of, or in conjunction with, labyrinth-type seals, and at various locations in the apparatus. Brush seals are also being utilized at locations subjected to increasing temperatures and pressures. A typical brush seal comprises a plurality of elongated bristles formed of a ceramic or metal material disposed between one or more backing plates. The brush seal is conventionally fixed to one component, e.g., a fixed component, with the bristle tips projecting from the seal to engage another component, e.g., a rotatable shaft, to form a seal therewith.
Current brush seals however, cannot withstand operating environments in which the temperatures are above 1200xc2x0 F. Application of brush seals to areas of the turbine having higher temperatures has thus been inhibited by this temperature limitation. For example, in hot gas path applications in gas turbines, such as bucket tip sealing, operating temperatures can be 1800xc2x0 F. or higher. Consequently, there is a need for an improved brush seal for use in applications at high temperatures.
In accordance with a preferred embodiment of the invention, a film-cooled high temperature brush seal is cooled by jets of a cooling medium injected adjacent the upstream side of the brush seal; that is, in one preferred embodiment, a thin film of cooling medium serving as a thermal insulator flows along upstream surfaces of the bristles and past the bristle pack to maintain temperature of the bristles below a predetermined temperature, for example, 1200xc2x0 F. The cooling flow protects the bristles from the high temperature working fluid medium. A typical application of this preferred embodiment includes provision of a brush seal formed in the shroud surrounding bucket tip covers of a gas turbine. The buckets lie in the hot gas path with the bristles projecting from the shrouds for engagement with the rotating components, e.g., bucket tip covers. Nozzles are circumferentially spaced one from the other about the shrouds for flowing jets of a cooling medium in a generally radial direction to provide a thermal insulating film of the cooling medium on upstream surfaces of the brush seal bristles and along the rotating component, i.e., the bucket tip covers. In conjunction with a typical brush seal arrangement, i.e., a brush seal having a pair of backing plates on opposite sides of the bristle pack and with the upstream backing plate spaced from the bristle pack, a spacer or a flange between the upstream backing plate and the bristle pack is provided. The spacer or flange includes a plurality of circumferentially spaced nozzles to flow the cooling medium between the upstream backing plate and the upstream face of the bristle pack to reduce the temperature of the bristles to well below the temperature of the hot gas stream; that is, the nozzles provide a thin, thermally insulating film of cooling medium between the bristles and the hot gas path. Additionally, the cooling medium flows along the bucket tip covers, cooling the covers and buckets.
In another preferred embodiment of the invention, the nozzles are arranged upstream of the brush seal and open through the stationary component. For example, the nozzles may be arranged upstream of the upstream backing plate and open through the shroud. The nozzles preferably lie in communication with a plenum containing the cooling medium, e.g., air. The jets of air thus flow along the forward surface of the backing plate into the gap between the upstream backing plate and the rotating component, and form a thin-film layer along the upstream faces of the bristles adjacent their tips. The thin film of air then flows through the juncture of the bristle tips and the bucket covers. In another form, the nozzles may be angled from the shrouds to direct the jets of cooling medium directly at the juncture of the bristle tips and the rotating component. The nozzles may also be formed through the upstream backing plate such that the jets of cooling medium are angled or directed onto the juncture of the bristle tips and the rotating component.
In still another preferred embodiment of the invention, sealing apparatus comprises first and second components movable relative to one another and defining a gap therebetween for flowing a fluid medium at a high temperature, and a brush seal carried by the first component for disposition between the first component and the second component and sealing the gap between high and low pressure regions on respective opposite sides of the seal. The brush seal includes a plurality of projecting bristles having free ends terminating in bristle tips in engagement with the second component so as to form a seal between the components to minimize fluid flow from the high pressure region through the gap to the low pressure region, and means for forming a thin layer of cooling medium along a surface portion of the bristles to thermally insulate the bristles from the high temperature fluid medium.
In a further preferred embodiment of the invention, a rotary machine comprises a rotatable component and a component that is fixed against rotation, or stationary. The components are disposed about an axis, with a brush seal carried by one of the components including a plurality of bristles projecting from the one component and having free ends terminating in bristle tips in engagement with another of the components to minimize flow of a high temperature fluid from a high pressure region on one side of the brush seal to a low pressure region on an opposite side of the seal. A plurality of nozzles are carried by one component for directing a cooling medium toward a juncture of the bristle tips and the other component to form a layer of cooling medium adjacent a surface of the bristles on an upstream side thereof to thermally insulate the bristles from the fluid.